1. Field of the Invention
The present invention relates to an etching method.
2. Description of the Related Art
The plasma etching apparatus which uses reaction components in gas plasma has attracted attention these days as a means for etching various kinds of thin films. This etching apparatus can make the complicated manufacturing process of semiconductor elements simple and automatic. Further, it can create semiconductor elements of micropattern which high precision.
According to this etching apparatus, a block electrode made of aluminium is located at the lower portion of an air-tight container which is communicated with a vacuum means. Another block electrode made of aluminium and provided with an electrode made of amorphous carbon is located above the lower block electrode in the air-tight container. RF power source is connected to the electrode made of amorphous carbon and the upper block electrode made of aluminium. A substrate to be treated, that is, a semiconductor wafer is mounted on the lower block electrode made of aluminium. Power is applied to the RF power source and to the electrodes, while a desired processing gas is supplied between the upper and lower block electrodes at the same time. The processing gas is thus changed to plasma by the electric power applied. The surface of the semiconductor wafer is etched by the processing gas which has been changed to plasma.
In the case of the above-mentioned plasma etching apparatus, however, electric power is applied to the electrodes to change the processing gas to plasma. The semiconductor wafer is heated by energy created at the time when the processing gas is changed to plasma. The resist layer on the semiconductor wafer is damaged by this heat. It is therefore needed that the semiconductor wafer is cooled while it is being etched. Preliminarily-opened Japanese Patent Application Sho 61-20622, for example, discloses a technique of cooling the semiconductor wafer and the like. According to this technique, the semiconductor wafer is mounted on the electrode while it is pressed along its peripheral rim. A cooling gas is supplied between the semiconductor wafer and the electrode to spread from the center of the wafer to the periphery thereof so as to cool the semiconductor wafer. The cooling gas is supplied, in this case, to the underside of the semiconductor wafer only to spread from the center of the wafer to the periphery thereof. Therefore, the pressure and flow rate of the cooling gas differ with different positions on the underside of the semiconductor wafer. The semiconductor wafer is thus sometimes lifted from the electrode to make smaller its area which is contacted with the electrode. This makes it impossible to apply uniform etching to the whole surface of the semiconductor wafer.
Electric power is applied to both of the block electrodes in the conventional plasma etching apparatus. The upper block electrode is heated to 150.degree. to 180.degree. C. in this case. The electrode made of amorphous carbon and the upper block electrode provided with this amorphous-carbon-made electrode are expanded by heat. Amorphous carbon is different from aluminium in thermal expansion coefficient. This causes the amorphous-carbon-made electrode to be cracked.
Japanese Patent Publication Sho 62-48758 discloses a technique of cooling the electrodes to eliminate the above-mentioned drawback. According to this technique, electric power is applied to the block electrodes while the amorphous-carbon-made electrode is being cooled. This prevents the electrode from being cracked. When electric power is applied to the block electrodes while the electrode is not being cooled, however, the amorphous-carbon-made electrode is still cracked because of thermal expansion.